The present invention relates to a structure of multilayer electronic elements for use widely in electric products and a manufacturing method therefor, and more particular to a multilayer ceramic chip capacitor and a manufacturing method therefor.
A multilayer ceramic chip capacitor is usually manufactured by the following process.
Initially, a coating material is prepared in which dielectric particles and a binder are dispersed in a solvent. The surface of a support member, made of polyethylene terephthalate or the like, is coated with the coating material so that a green dielectric layer is formed. Then, a conductor pattern (a green internal electrode portion) for the internal electrode is formed on the green dielectric layer. The green internal electrode portion is usually formed by, for example, screen-printing conductor paste. Then, the support member is separated from the green dielectric layer which has the green internal electrode portion. While the positions of the green internal electrode portions are being aligned, a plurality of the green dielectric layers are laminated. Thus, a green laminate is formed.
The obtained green laminate is applied with pressure and compressed, and then cut into a predetermined size. Thus, green chips (divided green laminates) are manufactured. Then, the green chips are burned at predetermined temperatures in a predetermined atmosphere so that sintered bodies are obtained. Then, paste for forming external electrodes is applied to ends of the sintered body so that a multilayer ceramic chip capacitor is manufactured.
FIG. 4A is a schematic view showing the internal structure of the green laminate realized during the process for manufacturing the multilayer ceramic chip capacitor. As shown in FIG. 4A, the multilayer ceramic chip capacitor is constituted by laminating and burning dielectric layers 62 each having a conductor pattern 61 for the internal electrode.
As shown in FIG. 5, the multilayer ceramic chip capacitor is constituted by alternately laminating internal electrodes 61 connected to external electrodes 63 disposed opposite to each other. The green internal electrode portions 61 are laminated on the green dielectric layer as follows: In FIG. 4C which is a cross sectional view taken along a first cutting direction x-xxe2x80x2 shown in FIG. 4A, the green internal electrode portions 61 are aligned through green dielectric layers 62. In FIG. 4B which is a cross sectional view taken along a second cutting direction y-yxe2x80x2, the green internal electrode portions 61 are alternately laminated. The green dielectric layers 62 are cut along cutting lines 64 so that green chips are obtained.
The foregoing structure is formed such that the green internal electrode portions 61 are formed and laminated on the green dielectric layers 62. As shown in FIGS. 4B and 4C, spaces 65 are formed among adjacent green internal electrode portions in the green internal electrode layers. That is, first portions 66 in which the green internal electrode layers and green dielectric layers are alternately laminated and second portions 67 coexist in the green laminate, the second portions 67 being laminated through spaces interposed between upper and lower green dielectric layers. When multilayer ceramic chip capacitors are manufactured by burning the green laminate, the burning process is performed in a state in which the spaces 65 adjacent to the external electrodes are compressed, as shown in FIG. 5. Therefore, the internal electrodes are not flush with one another. That is, the ends of the internal electrodes are warped, causing the thicknesses to be made different among the ends and the central portion.
The degree of compression of the spaces 65 shown in FIGS. 4B and 4C is raised in proportion to the number of laminated layers. Therefore, stepped portions between the first portions 66 and the second portions 67 are enlarged excessively. Thus, the first portions 66 in the form of a laminate which is constituted by dint of hermetic contact between the green internal electrode layers and the green dielectric layers are greatly raised. Since the first portions 66 are pressed and compressed under high pressures as compared with those applied to the second portions 67, the densities of the first portions 66 and those of the second portions 67 are made to be different from one another. As a result, chip capacitors, which are final products, are deformed, cracks are formed and delamination takes place.
If the thickness of the green dielectric layer is reduced to achieve size reduction and enlargement of the capacity of the capacitor which have been required in recent years, the green dielectric layer can easily be cut in the stepped portion. Therefore, there arises a problem of, for example, short circuit occurring between the internal electrodes.
To overcome the problem caused from the rise of the green internal electrode portion, a variety of suggestions have been made.
In Unexamined Japanese Patent Publications 52-135050 and 52-133553, structures have been suggested in each of which a green dielectric space sheet having a gap corresponding to the green internal electrode portion is interposed in the green laminate so as to prevent a stepped portion.
The dielectric green space sheet must have the same thickness as that of the green internal electrode portion. If the thickness of the green internal electrode portion is 10 xcexcm or smaller, the green dielectric space sheet cannot accurately be punched to have the same shape as that of the pattern of the internal electrode so as to be inserted as described above. What is worse, processes for laminating some hundreds of layers must be performed such that insertion of the dielectric space sheet is performed for each layer. Therefore, mass production cannot easilybe performed.
A similar method has been disclosed in Unexamined Japanese Patent Publication 53-42353, in which recesses are formed in the portions of the green dielectric layers corresponding to the internal electrodes. Thus, the green internal electrode portions are embedded in the recesses to eliminate the spaces in the green laminate so as to flatten the structure. Another method has been disclosed in Unexamined Japanese Patent Publication 61-102719 in which the green internal electrode portions and the green dielectric sheets are punched to have predetermined shapes to alternately be laminated so as to eliminate the spaces in the laminate. Thus, the structure can be flattened. Each of the above-mentioned suggestions, however, requires a very thin green dielectric sheet to be handled. Therefore, mass production cannot easily be performed.
In Unexamined Japanese Patent Publication 52-135051, a method has been suggested in which a coating process for forming the green internal electrode portions is performed. Then, the space portions are coated with the green dielectric layers to flatten the surfaces of coating so as to laminate the layers. However, seepage of the pattern and erosion by dint of the solvent easily take place vertically or between the adjacent green internal electrode portions and the green dielectric layers. If the thickness of the green dielectric layer interposed between the green internal electrode portions formed vertically is reduced, the boundaries between the green internal electrode portions and the green dielectric layers are obscured by dint of the seepage of the pattern and erosion of the solvent. In this case, there is apprehension that a problem of short circuit between the internal electrodes arises.
Although the techniques of flattening the internal portion of the laminate to eliminate the spaces have been suggested, the foregoing structures have not been put into practical use because the thin green dielectric sheet cannot easily be handled.
In Japanese Patent Publication No. 2636306 and Japanese Patent Publication No. 2636307, techniques have been suggested in which the green internal electrode portions are first formed on the support members. Then, the green dielectric layers are formed by a coating process so as to embed the green internal electrode portions in the green dielectric layers. Thus, the surfaces of the internal electrode are flattened so that thin layers each having a thickness of 18 xcexcm is formed.
The above-mentioned method, however, cannot easily prevent rise of the green internal electrode portion if the thickness of the green dielectric is furthermore reduced.
As described above, the conventional methods are effective in only a case where the green dielectric layer has a relatively large thickness. If the thickness of the green dielectric layer is reduced, there arises problems of difficulty in performing mass production and unsatisfactory machining accuracy. Moreover, the surface of the laminate cannot be flattened.
Although the multilayer ceramic chip capacitor has been described, the other multilayer ceramic electronic elements encounter similar problems when the thickness of each layer is reduced.
At present, multilayer ceramic electronic elements, and more particularly multilayer ceramic chip capacitors are required to have small sizes because apparatuses incorporating the foregoing electronic elements are required to have reduced sizes and weights. Therefore, the thicknesses of all laminated layers of the multilayer ceramic electronic element must be reduced. However, there is apprehension that a multiplicity of the problems including the short circuit between the internal electrodes arise owning to the foregoing structure.
Accordingly, an object of the present invention is to provide a multilayer ceramic electronic element having a small size and satisfactory reliability and which can easily be manufactured and a method of manufacturing the multilayer ceramic electronic element.
To solve the foregoing problems, the present invention is characterized by the following structures:
A multilayer ceramic electronic element comprises: ceramic dielectric layers; internal electrode layers; and external electrodes for establishing connection with the outside such that the ceramic dielectric layers and the internal electrode layers are alternately laminated, wherein the internal electrode layer has an internal electrode portion and a dielectric portion which are continuously flushed with each other, and an end of the internal electrode portion is connected to the end external electrode without any curvity.
Further, an multilayer ceramic electronic element as mentioned above, in that the thickness of an internal electrode in each of the internal electrode layers is not larger than 1.2 xcexcm, and the thickness of ceramic dielectric substance interposed by the internal electrodes is not larger than 2 xcexcm.
Furthermore, multilayer ceramic electronic element as mentioned above, wherein at least fifty ceramic dielectric layers and internal electrode layers are alternately laminated.
A method of manufacturing a multilayer ceramic electronic element, comprises the steps of: forming a green internal electrode portion by thermally transfer-printing, on a green dielectric substances formed on a support member, a thermal transfer conductor material by a thermal transfer printing method; and forming a green dielectric portion by thermally transfer-printing, on the surface of the green dielectric layer in which the green internal electrode portion is not formed and which is flush with the green internal electrode portion, a thermal transfer dielectric material by a thermal transfer printing method so that a substantially flat green internal electrode layer is formed.
Further, in a method of manufacturing a multilayer ceramic electronic element, the green dielectric layer formed on the support member is formed by a thermal transfer printing method using a thermal transfer dielectric material.
Furthermore, in a method of manufacturing a multilayer ceramic electronic element, the thermal transfer conductor material is formed by sequentially laminating, on the support member, a separation layer mainly composed of wax, a conductor layer mainly composed of thermoplastic resin, wax and conductor particles or the thermoplastic resin and the conductor particles and an adhesive layer mainly composed of thermoplastic resin and wax or the thermoplastic resin and the thermal transfer dielectric material is formed by sequentially laminating, on the support member, a separation layer mainly composed of wax, a dielectric layer mainly composed of thermoplastic resin, wax and dielectric particles or the thermoplastic resin and the dielectric particles and adhesive layer mainly composed of thermoplastic resin and wax or the thermoplastic resin.
Furthermore, in a method of manufacturing a multilayer ceramic electronic element, the surface of a green internal electrode layer, which incorporates a green internal electrode portion formed on the surface of a green dielectric layer formed on the support member by a thermal transfer method and a green dielectric portion, is subjected to a calendering process so that the surface of the green internal electrode layer is flattened.
Green internal electrode portions in a green laminate which is a precursor of a multilayer ceramic electronic element must be formed as follows: spaces which are formed between adjacent internal electrodes are eliminated so as to form substantially flat green internal electrode layers. Moreover, the thicknesses of burned ceramic dielectric layers must be reduced. Therefore, a laminating process is performed such that a thermal transfer conductor material and a thermal transfer dielectric material are used to form green internal electrode portions and green dielectric portions by a thermal transfer printing method. Thus, green internal electrode layers are formed. Also the green dielectric layers can be formed by the thermal transfer printing method.
In general, the thermal transfer printing method has the following advantages: no drying process is required because a dry process is performed such that a thermal transfer sheet manufactured previously is used to form a pattern. Moreover, a necessity of making a new printing plate, which is required for the screen printing method for the purpose of changing the pattern, can be eliminated. Thus, an arbitrary pattern can quickly be formed. When the thickness of a pattern is reduced, seepage occurring when the screen printing process is performed can be prevented. As a result, an accurate pattern can easily be formed. Therefore, when the thermal transfer printing method is employed to form the green internal electrode layers, the green internal electrode portions and the green dielectric portions can easily successively be formed. Also their boundaries are free from seepage from the green internal electrode portions and the green dielectric portions. Thus, the thin layers can easily be handled and the structure can be simplified. Therefore, a reliable and compact multilayer electronic element can easily be manufactured.
The thermal transfer printing method is performed such that a thermal transfer dielectric material or a conductor material is brought into hermetic contact with the printing surface of a medium, for example, a green dielectric layer, which must be printed. Then, a heating unit, such as a thermal head, is operated to heat the thermal transfer member from the rear side of the same so that a required shape is obtained by the printing method.